This invention relates to an in-tank fuel pump mounted within a fuel tank of an automobile and more particularly to means for removing bubbles generated in the pump.
FIG. 1 is a sectional view showing a conventional in-tank fuel pump disclosed in Japanese U.M. Laid Open No. 61-99692, for example, and in the figure, 1 is a main body defining an outer shell of the pump, 2 is a cylindrical yoke, 3 is a cover placed over one end of the yoke 2, 3A is a discharge pipe projecting toward the outside of the cover 3 for discharging the fuel in the fuel chamber 4 outside of the main body 1, 3B is a discharge passage projecting toward the inside of the cover 3 for introducing the fuel in the fuel chamber 4 into the discharge pipe 3A, and 3C is a relief port formed in the cover 3 and located in the upper portion of the fuel chamber for relieving bubbles in the fuel chamber 4 to the exterior. 5 is a bracket placed over the yoke 2 and positioned by a step portion 2A, 5A is a first through hole formed in the bracket 5 for allowing the insertion of the commutator 14, 5B is a second through hole for supplying the fuel pumped by the impeller 16 to the fuel chamber 4, 5C is an injection pipe formed in continuation with the second through hole 5B of the bracket 5, 6 is a pump cover embedded into the bracket 5 and placed over the yoke 2, 6A is a suction or fuel inlet pipe projecting toward the outside of the pump cover 6 for sucking the fuel to the pump chamber 7, 8 is a first metal bearing inserted into the recessed portion of the cover 3 and secured by a metal holder 9, 10 is a second metal bearing inserted into the recessed portion of the pump cover 6 and 11 is a motor which comprises a main shaft 12 journaled at the opposite ends by the first metal bearing 8 and the second metal bearing 10. An armature 13 with the commutator 14 is mounted on the main shaft 12 and a magnet 15 secured at the inside of the yoke 2 so as to oppose the armature 13. 14A is a plurality of projecting portions which project from the commutator 14 substantially parallel to the main shaft 12. 16 is an impeller inserted into the main shaft 12 and the projecting portions 14A of the commutator 14, the outer periphery of which is formed into a blade. 17 is a brush assembly for supplying electrical power to the commutator 14, and 18 is a terminal connected to the brush assembly 17 for supplying electrical power from the exterior.
The description will now be made as to the operation of the conventional fuel pump as above-constructed.
Firstly, when external electrical power is supplied to the brush assembly 17 through the terminal 18, the motor 1 is electromagnetically driven to rotate the armature 13. Therefore, the impeller 16 mounted on the main shaft 12 is rotated by the rotational force transmitted through the projecting portion 14A of the commutator 14. This causes the fuel to flow from the suction pipe 6A into the pump chamber 7, then the fuel is pumped by the blade formed on the outer periphery of the impeller 16 and transferred under pressure to the fuel chamber 4 through the second through hole 5B. The fuel thus filled in the fuel chamber 4 is pressurized by the pressure of the fuel pumped by the impeller 16, and pumped out from the discharge pipe 3A to an unillustrated automotive carburator for example.
In the conventional in-tank fuel pump as above described, the blade shaped portions at the outer periphery of the impeller 16 agitate the fuel by the rotation of the impeller 16 and generate bubbles. When the amount of the bubbles generated is increased or when the automobile makes a tight turn with only a slight amount of fuel remaining in the tank, the air within the tank is temporarily sucked into the pump chamber, making the interior of the pump chamber fill with a vapor-liquid mixture. If the amount of vapor becomes too great, the blade of the impeller 16 rotates in the vapor, posing the problem that the pumping action is lost and the fuel cannot be pumped to the automotive carburator.